The present invention relates to devices assisting the driving of rail vehicles.
French Patent No. 83 03 706 filed on Mar. 7, 1983 in the name of Mr Jean-Pierre Malon described a device for the driving and/or control of a rail vehicle, comprising means for dividing the route intended for the vehicle into successive space intervals, forming at least one program inscribed within the route, and means for detecting the limits of the space intervals, intended for controlling the means for the piloting and/or control of the vehicle.
The successive space intervals are delimited by markers arranged along the route, and take the form of codes identifying this at least one program, the detection means having at least one sensor for reading the codes and means for discriminating between the output signals of the sensor as a function of the operating conditions for the purpose of determining the program to be executed.
The known device of the abovementioned type ensures the safe movement of trains on an underground network.
The control of the train is ensured by the knowledge of two essential data items:
the state of occupation of the track downline from the moving vehicle in question (signalling); and
the limiting possibilities of the track at the location of the moving vehicle (speed limit polygon).
In the device described in the abovementioned patent, there is transmission of the signalling state by means of carrier frequencies injected into the rails.
The markers arranged on the ground determine the speed profiles. They are read on board the train by on-board sensors.
Moreover, French Patent No. 90 05 285, filed on Apr. 25, 1990 in the name of ACELEC, makes known a device for automatic speed control which employs "retractable" markers when a plurality of program can be read.
In the two instances mentioned above, the control of the speed is obtained by a measurement of the running time between two successive markers.
Whatever the known control device to be used, the safety of the device is based on perfect detection of the ground markers.
In fact, an undetected marker allows, locally, an overspeed in relation to the speed which would be allowed in the event of normal detection of all the markers.
For example, a detection failure eliminating one marker out of two over a constant-speed zone allows a doubling of the maximum speed of the train.
In contrast, the inopportune detection of "phantom" markers is not detrimental to safety, since this detection of additional markers which do not actually exist, artificially decreases the maximum permitted speed.
It is therefore necessary to execute a safety validation of the detection of all the markers of each line, whether these markers are stationary or retractable.